Hi rdhot, if the original tank is 8 oz., if you stick to the original tank shape then usually a 10 oz. will fit in with no mods. I would think to get a 12 oz. tank in you would need to fire up the dremel and widen the sides or the top a bit. A 10 oz. tank is really all you need for a 46 size engine. If you are at the field by yourself no big deal but, if there are others waiting to fly then flying for longer than a 15 minute flight may be infringing on flight line etiquette.